[BSRAM] Add Backup SRAM support for LYRA boards and relative test
Uses the BSRAM driver in the kernel to initialize the Backup SRAM and the .preserve
section based on the last reset cause. Preserved variables need to be declared with the PRESERVE
macro attribute that automatically places them in the .preserve
section.
To change the value of a preserved variable, a WriteEnableLock
must be acquired.
Also a test for the backup SRAM has been implemented.